I used the jailbreak from here:
https://www.mobileread.com/forums/showthread.php?t=88004
The newest is v0.10. This may confuse some people who think that v0.9 is newer tha v0.10. Use the one that contains 3.2.1 in the file name inside the zip file.
Only put one update*.bin file on your kindle USB drive at a time. If you have the correct jailbreak key installed, when you put an update file signed with the jailbreak key for your kindle version on your USB drive, the "update your kindle" menu item should be enabled.